When designing a highly available architecture, what is the difference between vertical scaling (scaling-up) and horizontal scaling (scaling-out)?

Answer options:

A.Scaling up provides for high availability whilst scaling out brings fault-tolerance.
B.Scaling out is not cost-effective compared to scaling up.
C.Scaling up adds more resources to an instance, scaling out adds more instances.
D.Autoscaling groups require scaling up whilst launch configurations use scaling out.

Correct Answer – C
In high availability architectures, Autoscaling is used to give elasticity to the design. Horizontal scaling (scaling-out) uses Autoscaling groups to increase processing capacity in response to changes in preset threshold parameters. It could involve adding more EC2 instances of a web server. Vertical scaling (scaling-up), which can create a single point of failure, involves adding more resources to a particular instance to meet demand.
https://docs.aws.amazon.com/autoscaling/plans/userguide/what-is-aws-auto-scaling.html
Option A is INCORRECT. Scaling-up does not provide high availability. Adding more resources to one instance is often not a best-practice in architecture design.
Option B is INCORRECT. Scaling-out is cost-effective since it involves adding more resources in response to demand and reducing resources (scaling down) when demand is low.
Option D is INCORRECT. All Autoscaling groups require a launch configuration based on what resources would be provisioned or deprovisioned to meet predefined parameters.